Piston blank and method of manufacturing pistons



NOV: 1, 1932. MlLLER 1,885,463

PISTON BLANK AND METHOD OF MANUFACTURING PISTONS Original Filed Nov. 18, 1929 2 Sheets-Sheet 1 4 7 INVENTQOR. BY Aim I M 1- 0h);

- ATTORNEYS.

Nov. 1, 1932;. D. MILLER 1,885,463

PISTON BLANK AND METHOD OF MANUFACTURING PISTONS Original Filed Nov. 18. 1929 2 Sheets-Sheet 2 Fig. 7 F1 8- E:

IN VEN TOR- A TTORNEYS.

Patented N ovnl, 1932 i UNITED STATES PATENT OFFICE norm mrnnnn, on nnrnorr, MICHIGAN, ASSIGNOR- T was TOLEDO 'ALLOYED OASTINGS COMPANY, or. 'ronnno, 01110, A oonroaa'rron or 01110 PISTON BLANK AND METHOD ,OF MANUFACTURING PISTONS Original application filed November 18, 1929, Serial No. 407,852. Divided and. this application filed July 22,

' 1930. Serial No. 469,826.

This invention relates to pistons of the flexible skirt type, but more to pistons of alloy containing aluminum, where it is necessary to compensate'for the relatively great expansion and contraction of the metal.

Heretofore, aluminum pistons have been cast in temporary sand molds, or in perma-- the core is made up of several parts which have to be carefully assembled in order that the interior of the piston be of the desired size and shape, and, therefore, after the piston is cast these parts must be lndlvidually taken from the mold. Obviously, this mode of manufacture does not lend itself to eflicient quantity production of pistons. Another outstanding objection to former methods of I piston production resides in the finishing of the piston after it is cast, a considerable number of steps being required to produce the finished article.

An object of this invention is to improve the method of manufacturing a piston of aluminum alloy or similar materials, which permits the use ofa permanent mold and a non-collapsible core so thatafter the piston is cast the core may be removed in a single operation.

Another object is to produce a piston blank having the new and improved features of con; struction and arrangement hereinafter described.

Other objects and advantages will appear as the description proceeds, and for purposes of illustration, and not of limitation, the invention is shown on the accompanying drawings, in which:

Fig. 1 is a side elevation of the rough piston casting partly in section showing the plston after being taken from the mold;

Fig. 2 is ,a side elevation of the, finished piston; I Fig. 3 is a longitudinal sectional. elevation on the line 3-3 of Fig.2;

Fig. 4 is a longitudinalsectiona'l elevation on the line 4-4 of Fig. 3;

" Fig. 5 is a sectional elevation on the line 5-5 of Fig. 6; I

Fig. 6 is a transverse section on the line 6-6 of Fig. 2;

Fig. 7 is an end view of the rough piston casting shown in Fig;1;

Fig. 8 is a longitudinal section on the line 88 of Fig. 6;

Fig. 9 is a diagrammatic view showing in exaggerated form the position of the inner skirt relative to the outer skirt when pressure is exerted in the direction of the arrows; and

' Fig. 10 is a diagrammatic view showing the relative position of the parts whereforce is exerted in the direction of the arrows.

--This application constitutes a division of my copcnding' application, Serial Number 407,852, filed November 18, 1929, entitled Compensating piston, which issued as Patent No. 1,774,064 on August 26, 1930.

Referring to the drawings, the piston comprises a circular skirt 1 and head 2, the circular wall of the latter being sufliciently thick to allow machining of relatively deep ring grooves 7, and still maintain sufiicient wall for the required strength. Diametricals lyoppose'd openings 3 are provided in the skirt 1, and through these openings extend piston pin bosses 4. The bosses 4 are connected by an arm 4 integrally with the flat and circular side wall portions of the head 2. For affording additional strength to the fiat portion of the head 2, and joining the arms 4,

the ribs 4 integral with the head.

As particularly shown in Figs, 3 and-5, the integral surfaces of the bosses 4 and arms 4 are substantially unbroken in a longitudinal direction providing a plane at substantially right angles to the internal surface of the flat portion of the head 2. This feature isof importance in the casting of the piston as it eliminates under-cuts which militate against the use ofa unitary core.

Within the outer skirt 1 is an inner skirt 8, which is in substantially*concentric relation to the outer skirt and is cast integral with the head 2 and bosses 4, as will be hereinafter described-. The outer skirt 1 and inner skirt 8612a severed fromthe head 2. providing a space 5 therebetween so that the outer skirt gregate thickness of the outer skirt 1, inner skirt 8, and space therebetween, is equal to the thickness of the circular wall of the head 2. I v

In the finished form of the piston the inner skirt 8 provides two separate portions, each portion being integral with a boss 4 and with the outer skirt 1 at points remote from the respective boss. The inner skirt 8 could be a complete circle with one or more points of attachment to the outer skirt 1, but the shown division of the inner skirt has been made to give the outer skirt required support 'andto save weight in metal. The length of the inner skirt is governed by the desired strength, and the sections of the inner skirt after machining may be termed struts or supports.

The outer skirt 1 is divided into two separate portions, and in this instance diagonal slits 7 in the region of the bosses 4 are formed, and this division maybe made either under the bosses 4, or between the inner skirt or strut portions 8.

In use it will be manifest that the head 2 does not contact with the walls of the cylinder, but the usual rings in the grooves 6 form the contact between the head and cyl-v inder wall. By virtue of the above construction the skirt maintains substantially uniform contact with the cylinder walls under all conditions. Although this invention is not confined to the use of an aluminum alloy piston, it is of particular use when the piston contains aluminum which has considerable propensity to expansion when subjected to heat. When heated the outer skirt 1 will, of course, expand circumferentially as the cylinder walls limit its expansion in a radial direction. I

In order to compensate for the expansion of the skirt 1, thereby to limit the pressure on the cylinder walls, the inner skirt portions or strut members 8 perform their. important function. When these members 8 are heated,

due to their curvature they expand outwardly toward the outer skirt 1, and in this manner limit expansion of the outer skirt 1. It is, therefore, apparent that the maximum pressure on the cylinder walls caused by the expansion f the piston is limited by the flexibility of the inner and outer skirts, and such flexibility is governed by the thickness of the walls, which is chosen according to commercial requirements. The outward bowing of the inner skirts or strut members 8 is clearly demonstrated in exaggerated form in Fig. 10, 'in which arrows indicate pressure directed on diametrically opposed points. In

order further to indicate the flexibility of the piston, Fig. .9 indicates in exaggerated form the relation of the parts when pressure is exerted thereagainst at diametrically opposed point-s indicated by the arrows in conneetion therewith in the region of the. bosses 4. v

Another feature of outstanding importance in connection with this invention is the method by which this piston may be manufactured. The method is of particular importance in that it lends itself to efficient and satisfactory large scale production. As mentioned heretofore, no little difiiculty has been encountered in the successful manufacture of pistons of aluminum alloy, or the like, on a commercially efiieient basis. The above described piston may be cast in a permanent mold with the med a one-piece unitary core.

As above explained, the uniform, smooth, internal surface of the bosses 4 and arms 4* permit the core to be readily withdrawn from the interior of the piston in one operation. This is also made possible by having the aggregate thickness of the inner skirt, outer skirt, and space therebetween, substantially equal to, or less than, the thickness of the circular wall of the head 2 so that the partsof the core are in straight line relationship, and can be a one-piece structure which can be conveniently withdrawn from the mold. As the piston is taken from the mold it has an appearance similar to that shown in Fig. 1, in which the inner skirt portions 8 and outer skirt 1 are integral with the head 2.

The rough casting is then mounted on an expanding chuck to which rotation is imparted, the outerside diameter of the piston is then turned,'th e head faced, the skirt cut to dimension. and the piston ring grooves 6 formed, and thereafter a turning tool applied to the pistonv casting at substantially the point 9 (Fig. 1) severs both the inner and outer skirt portions 8 and 1, respectively,

from the head 2, leaving the outer skirt supported by the inner skirt which remains attached to the bosses 4 and arms 4% The next step in the manufacture consists in reaming the bosses, and the final operation resides in dividing the outer skirt 1 longitudinally either between the supporting elements, or struts 8, or. under the bosses 4 to provide two separate sections.

From the above description it will be quite ment, it is to be understood that modifications of the structure shown may be made by those bosses from the w .skilled in this art without departing from my invention, as expressed in .the following claims.

What I claim as new and desire to secure by Letters Patent is:

ton.

all of the cup-shaped pis- In testimony whereof I have hereunto signed my name to this 1. A piston blank having a head having a 7 depending circular wall, a circular skirt section Within the outside diameter of the circular wall and having a free lower end, and an inner circular support section without the inside diameter of'circular wall of head and having a free lower end.

2. A piston blank comprising a head, a cylindrical outer skirt integral with said head and having a free lower end portion, a sup-' porting skirt integral with said head and disposed within and concentric to said skirt and aving a free lower end portion, and piston pin bosses integral with said supporting skirt and head, the inner sides of said bosses being substantially straight.

3. A piston blank comprising a head, a

skirt integral with and depending from said head and having a free lower end, a curved support integral with and depending from said head and concentric to said skirt, said curved support having a free lower end, piston pin bosses integral with said support, and an integral connection between each boss and said head, said connections being arranged inwardly of said support whereby said skirt and support may be severed from said head without severing said bosses.

4. A piston blank comprising an annular head, a skirt integral with and depending from said head having the outer surface there of substantially flush with the outer surface of said head, a curved support integral with and depending from said head and concention with the inner skirt and the disc portion of the cup-shaped piston, and then severing the inner and outer skirts from the wall of the cup-shaped piston.

6. The method of forming a piston comprising casting a cup-shaped piston with concentric outer andinner skirts and a pair of piston pin bosses respectively having an integral connection with the inner skirt and the disc poption of the cup-shaped piston with the inner sides of said connections being smooth and at approximately right angles to the disc-portionof the cup-shaped piston, and

severing the inner and outer skirts above the specification. DORR MILLER. 

